Why do you sometimes ignore the brawny bag boy at the supermarket, and other times sweetly request that he push your cart (while you contemplate the best way to throw him in the trunk and take him home)? Why does the attention you receive from the opposite sex always seem to take on either a feast or famine characteristic? Every one of these questions can be answered simply: hormonal fluctuations.

In order to gain a better understanding of how your hormonal fluctuations (particularly of estrogen, testosterone, and progesterone) affect your thoughts and actions, consider keeping a calendar of your menstrual cycle.

Days 1–8: On the first day of your period, you might feel like your body’s out of commission, but your brain is revving up for some serious hormonal spikes. During the next five days, your estrogen levels will begin to climb, making you keenly interested in interaction with others, relaxed and fulfilled by conversation, and talented in verbal and memory skills. As testosterone begins its ascent, your libido will gradually increase.

Days 9–13: Testosterone and estrogen are on dramatic upswings. By day 10, your testosterone levels will bring sexual thoughts to the forefront, so throwing that bag boy into your trunk with the eggs and escarole becomes a real possibility.

Estrogen will firm and plump your skin; make your digits, ears, and breasts more symmetrical; clear up your complexion; and brighten your lip color. It will sweeten the taste and smell of you and will prompt you to choose more feminine, frilly clothing that might show a bit more skin than is your norm. Your dreams and daydreams might be dominated by visions of sugarhunks dancing on you, and you’ll notice that you’ll get more glances and advances from men.

Other women, particularly beautiful ones, might receive some glares from your direction. You might find yourself trashing other females to male suitors and craving the company of guys over gals.

Days 14–20: On day 14, your egg will enter the fertilization zone, prompting the drop-off of estrogen and testosterone, along with an increase of progesterone. Your mind-set will shift from that of a sex-crazed vixen to that of a doting mother. Your verbal skills and clarity of thought might plummet, while your affinity for babies increases. You might feel more comfortable being alone than surrounded by people. A general sense of well-being will remain, while your desire to compete with other females decreases.

Days 21–28: As your brain experiences withdrawal from estrogen and testosterone, the sense of well-being you enjoyed for most of your cycle is not only a distant memory, but 1 in 25 of you will turn into depressed, even psychotic, versions of yourselves. You’ll be more likely to schedule consultations with astrologers, counselors, and psychologists, and your propensity for committing crimes and getting into car accidents will skyrocket. Sex will likely be the furthest thing from your mind, though a good romp could soften the irritability that causes men, children, and woodland creatures to scamper for their lives at the sight of you.